Thanks, I have some trepidation about Sunday, but it's too late to do anything to prepare beyond sleeping and eating well and staying healthy. My habit of signing up for long distance running events, while doing little running on other days, is probably not ideal.
Waste management will be a concern. One of the benefits of trail running is that when Nature calls, Nature is right there. I sometimes worry about carrying too much water more than running out. At the 2011 Marine Corps Marathon, I saw lines at porta-potties on the course. I'll do my best to cut weight before the start, but there's no way I will be standing in a line after the clock starts.
The plan this year is to give up my intention to run every step, instead taking walk breaks now and then to recover and eat and drink. I might try to keep the 4-hour pacer in view as long as possible. For the first few miles I expect to be stuck at the crowd's pace anyway.